Generally, a capacitively coupled plasma processing apparatus includes an upper electrode and a lower electrode disposed parallel to each other in a depressurizable processing vessel configured as a vacuum chamber, wherein a target substrate (e.g., a semiconductor wafer, a glass substrate, etc.) is mounted on the lower electrode. Electrons are accelerated by an electric field formed by a radio frequency voltage applied between the upper and the lower electrode and are made to collide with a processing gas. As a result of ionization by the collision between the electrons and the processing gas, a plasma is generated, and a desired process (for example, etching, deposition, oxidation, sputter, etc.) is performed on the surface of the substrate by radicals or ions in the plasma. Typically, a coaxial cable is used as a radio frequency power supply line through which the radio frequency power outputted from a radio frequency power supply is supplied to the electrode inside the chamber. A matching circuit is attached to an end of the coaxial cable. This matching circuit is an LC circuit which serves to match an impedance of the plasma (load) to that of the radio frequency power supply. The matching circuit has a single or plural variable capacitors therein and functions to control the capacity of variable reactance so as to minimize a reflection wave from the plasma (see, for example, Japanese Patent Laid-open Application No. 2005-109183).
Recent researches have found that, in the aforementioned capacitively coupled plasma processing apparatus, an impedance of a radio frequency transmission path, which ranges from a front surface (a surface in contact with the plasma) of an ungrounded electrode to a ground potential via the ungrounded electrode, is an important factor that determines an generation amount of harmonic waves or intermodulation distortion. Besides, it is also found that this impedance of the radio frequency transmission path influences a process performance. According to these researches, it is preferable to design each component of the apparatus, particularly, a radio frequency power supply system, such that the impedance of the radio frequency transmission path is of an optimum value or within an optimum range. However, in practice, there frequently occurs a mechanical difference in the radio frequency power supply system between apparatuses (particularly, the mechanical difference is likely to occur due to a difference in the length of the RF cable, the circuit constant of the matching circuit, or the like), and such mechanical difference in the radio frequency power supply system has a great influence on the impedance of the radio frequency transmission path.
In view thereof, a use of an inspection method is under consideration wherein the method involves directly measuring the impedance of the radio frequency transmission path by means of installing a jig of a impedance measuring unit on the electrode front surface inside the chamber in each apparatus; and making a determination that the process performance is normal (good) if the impedance value is within a specific range or that the process performance is abnormal (bad) if the impedance is out of the range. This inspection method does not necessitate plasma ignition or plasma generation, so it can be performed when shipping the apparatus or installing the apparatus at a target place. In the capacitively coupled plasma processing apparatus, however, the electrode front surface, which is in contact with the plasma while radiating radio frequency waves, is the most important part on the process and is the most vulnerable part as well. Therefore, installing the jig on this part is not preferable in the aspect of protecting electrodes and preventing particle generation.